Reconfigurable LNA for increased jammer rejection

ABSTRACT

A reconfigurable LNA for increased jammer rejection is disclosed. An exemplary embodiment includes an LNA having a tunable resonant frequency, and a detector configured to output a control signal to tune the resonant frequency of the LNA to increase jammer suppression. An exemplary method includes detecting if a jammer is present, tuning a resonant frequency of an LNA away from the jammer to increase jammer rejection if the jammer is present, and tuning the resonant frequency of the LNA to a selected operating frequency if the jammer is not present.

BACKGROUND

1. Field

The present application relates generally to the operation and design ofwireless devices, and more particularly, to the operation and design oflow noise amplifiers.

2. Background

High quality signal reception is especially important for the currentgeneration of portable devices. Typically, such devices provide multipleservices, such as wireless communication services and, for example,position location services that require the reception of globalnavigation satellite signals. For example, global navigation satellitesystems comprise a wide range of satellite positioning systems (SPS)that include the Global Positioning System (GPS) used in the UnitedStates, the GLObal Navigation Satellite System (GLONASS) used in Russia,the COMPASS navigation system used in China, the Galileo system used inEurope, and other regional positioning systems. Thus, the front end of awireless receiver needs to be carefully designed to reject interferingsignals and receive desired signals with high sensitivity.

To illustrate the problem, consider a GPS coexistence scenario where aportable device includes a GPS receiver and a cellular transmitter. Inthis GPS coexistence scenario, strong radio frequency signals can appearat the GPS receiver's front-end due to transmission on the cellularchannel. Such signals may jam the GPS receiver and thus interfere withGPS signal reception. To address this problem, GPS receiver designsusually provide high linearity and have a very low noise figure (NF).Providing this high level of performance also result in high powerconsumption. For example, to operate concurrently during strong Txjammer power and to avoid GPS local oscillator (LO) phase noise beingmixed down to the IF Band through reciprocal mixing, the GPS LO shouldhave very low phase noise, which may result in excessive powerconsumption.

Therefore, what is needed is a way to relax the LO requirements for lowphase noise when strong Tx Jammer power is present in a front endreceiver. It is therefore desirable to have a front end receiver withimproved jammer suppression so that the LO requirements can be relaxed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects described herein will become more readily apparentby reference to the following description when taken in conjunction withthe accompanying drawings wherein:

FIG. 1 shows an exemplary embodiment of a front end comprising a GPSreceiver that includes a reconfigurable LNA;

FIG. 2 shows an exemplary graph that illustrates the operation ofexemplary embodiments of a reconfigurable LNA for increased jammersuppression;

FIG. 3 shows an exemplary graph that illustrates the operation ofexemplary embodiments of a reconfigurable LNA for increased jammersuppression;

FIG. 4 illustrates an exemplary embodiment of an LNA with reconfigurableresonant frequency;

FIG. 5 illustrates an exemplary embodiment of a method for increasedjammer suppression in a GPS receiver; and

FIG. 6 shows an exemplary embodiment of a reconfigurable LNA apparatus.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of theinvention and is not intended to represent the only embodiments in whichthe invention can be practiced. The term “exemplary” used throughoutthis description means “serving as an example, instance, orillustration,” and should not necessarily be construed as preferred oradvantageous over other exemplary embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the exemplary embodiments of the invention. It will beapparent to those skilled in the art that the exemplary embodiments ofthe invention may be practiced without these specific details. In someinstances, well known structures and devices are shown in block diagramform in order to avoid obscuring the novelty of the exemplaryembodiments presented herein.

FIG. 1 shows an exemplary embodiment of a front end 100 comprising a GPSreceiver 102 that includes a reconfigurable LNA 104. For example, thefront end 100 is suitable for use in a wireless device to providecommunication and geographic positioning services. It should be notedthat the GPS receiver 102 may also comprises any suitable GlobalNavigation Satellite Systems (GNSS) receiver.

The front end 100 comprises a transmitter 106 configured to transmitdata from a digital baseband processor 108. The output of thetransmitter 106 is coupled to a power amplifier 110 that generates atransmit signal that is input to a duplexer 112. The output of theduplexer 112 flows to an antenna 114 for transmission.

The GPS receiver 102 receives low-level GPS signals and noise at antenna116 and these signals are input to the reconfigurable LNA 104. Asdescribed in greater detail below, exemplary embodiments of the LNA 104are reconfigurable so that its resonant frequency can be adjusted toprovide increased jammer suppression. In addition to providing increasedjammer suppression, the LNA 104 amplifies the received signals andpasses the amplified signals to a downconverter 118 that downconvertsthe GPS signals to baseband by utilizing a local oscillator (LO) signal120 generated by phase lock loop (PLL) 122, voltage controlledoscillator 124, and frequency divider 126. The downconverted GPS signalsare passed through a baseband filter 128 and then fed into the digitalbase band processor 108 that processes the filtered GPS signals todetermine position information.

During operation, the digital baseband processor 108 is aware oftransmissions from the transmitter 106 and the associated transmissionfrequency. Transmitted power from the transmitter 106 may feedback intothe GPS receiver 102 through the antenna 116 (as a self jammerillustrated at 136) to degrade GPS performance. In an exemplaryembodiment, the digital baseband processor 108 outputs a control signal130 that is input to the reconfigurable LNA 104. The control signal 130adjusts the LNA 104 to cause the resonant frequency of the LNA 104 to beshifted in frequency away from the frequency of the self jamming signal.Shifting the resonant frequency of the LNA 104 operates to increasejammer suppression.

In another exemplary embodiment, the digital baseband processor 108 isoperable to detect external jammers that may affect the performance ofthe GPS receiver 102. For example, the digital baseband processor 108may receive information about external jammers from other receivers (notshown) in a wireless device. When an external jammer is detected, thedigital baseband processor 108 outputs the control signal 130 to adjustthe LNA 104 so as to shift the resonant frequency of the LNA 104 awayfrom the frequency of the detected external jammer.

In another exemplary embodiment, the GPS receiver 102 comprises jammerdetector (JD) 132. The JD 132 is operable to detect jammers in the GPSband. When a jammer is detected, (i.e., either a self jammer or externaljammer) the JD 132 outputs a detection signal 134 to the LNA 104 toadjust the LNA 104 so as to shift the resonant frequency of the LNA 104away from the frequency of the detected jammer.

In still another exemplary embodiment, the digital baseband processor108 is operable to detect external jammers that may affect theperformance of the GPS receiver 102. For example, the digital basebandprocessor 108 may determine that jammers may be present based on thecurrent location of the device. For example, the current location of thedevice is determined from the received GPS signals and the digitalbaseband processor 108 operates to adjust the LNA 104 to suppresspotential jammers in the current geographic region determined by thecurrent position. If potential jammers exist based on the currentgeographic position, the digital baseband processor 108 outputs thecontrol signal 130 to adjust the LNA 104 so as to shift the resonantfrequency of the LNA 104 away from the frequency of the potentialjammers.

Accordingly, information about existing jammers or the potential forjammers is determined using one or more of the following techniques.

-   1. Jammer information is determined from knowledge of current    transmissions from the device and that are known by the baseband    processor 108.-   2. Jammer information is determined from knowledge of any external    jammers that are detected by another receiver at the device and that    are known by the baseband processor 108.-   3. Jammer information is determined from the current location of the    device which is known from processing received GPS signals.-   4. Jammer information is determined from the presence of jammers in    the GPS band detected by the jammer detector 132.

Thus, in various exemplary embodiments, the reconfigurable LNA 104 hasan adjustable resonance frequency that can be adjusted based on thedetection of self jamming or external jamming signals. For example, byshifting the resonance frequency of the LNA 104 to be farther away fromthe jamming frequency, additional jammer suppression is achieved. In thecase where no jammers are detected, the resonant frequency of the LNA104 can be restored for normal operation. It should be noted that thereconfigurable LNA 104 is not limited for use only in GNSS receivers asillustrated in FIG. 1, but is suitable for use with all types of frontend receivers.

FIG. 2 shows an exemplary graph 200 that illustrates the operation ofexemplary embodiments of a reconfigurable LNA for increased jammersuppression. In the graph 200, frequency is represented along thehorizontal axis and GPS L1 represents the frequency of received GPSsignals during normal operation. The resonant frequency of the LNA 104during normal operation is represented by the plot 202. A band of energy204 represents a self jammer due to a communication transmission. Forexample, the communication transmission at the shown frequency may occurin the United States and is referred to AWS(Tx), or Band 4 in UMTS-FDDoperation band. When the communication transmission is detected, eitherby the baseband processor 108 or the jammer detector 132, the LNA 104 isadjusted to move its resonant frequency to the left as shown by the plotline 206. As a result, increased jammer suppression is provided by theshifted resonant frequency characteristics of the LNA 104. For example,rejection of the jammer 204 before shifting the resonant frequency ofthe LNA 104 is illustrated at 208. The rejection of the jammer 204 aftershifting the resonant frequency of the LNA 104 is illustrated at 210.

FIG. 3 shows an exemplary graph 300 that illustrates the operation ofexemplary embodiments of a reconfigurable LNA for increased jammersuppression. In the graph 300, frequency is represented along thehorizontal axis and GPS L1 represents the frequency of GPS signalsduring normal operation. The resonant frequency of the LNA 104 duringnormal operation is represented by the plot 302. A band of energy 304represents a self jammer due to a communication transmission. Forexample, the communication transmission at the shown frequency may occurin Japan and is referred to as JPDC(Tx), or Band 11 in UMTS-FDDoperation band. When the communication transmission is detected, eitherby the baseband processor 108 or the jammer detector 132, the LNA 104 isadjusted to move its resonant frequency to the right as shown by theplot line 306. As a result, increased jammer suppression is provided bythe shifted resonant frequency characteristics of the LNA 104. Forexample, rejection of the jammer before shifting the resonant frequencyof the LNA 104 is illustrated at 308. The rejection of the jammer aftershifting the resonant frequency of the LNA 104 is illustrated at 310.

FIG. 4 illustrates an exemplary embodiment of an LNA 400 withreconfigurable resonant frequency. For example, the LNA 400 is suitablefor use as the LNA 104 shown in FIG. 1. The LNA 400 comprises an LC tankcircuit 402 operable to shift the resonant frequency of the LNA 400. Thetank circuit 402 comprises NMOS switch banks 404, 406 and capacitor bank408. During operation, the switch banks 404, 406 are used to control thecapacitance value provided by the capacitor bank 408 to shift theresonant frequency away from any detected jammer. Thus, the resonantfrequency can be shifted higher or lower depending on the settings ofthe NMOS switches 404, 406, which in one exemplary embodiment, arecontrolled by either the control signal 130 or 134. If no jammer isdetected, the capacitor bank 406 is set to allow normal LNA operation ata designated resonant frequency.

FIG. 5 illustrates an exemplary embodiment of a method 500 for increasedjammer suppression in a front end receiver. For example, the method 500is suitable for use with the GPS receiver 102 shown in FIG. 1 andreconfigurable LNA 400 shown in FIG. 4.

At block 502, a determination is made as to whether there are any selfjammers present to due device transmissions. For example, in anexemplary embodiment, the baseband processor 108 has knowledge ofcurrent transmissions from the device that may operate as self jammers.If a self jammer is present, the method proceeds to block 504. If a selfjammer is not present, the method proceeds to block 506.

At block 504, the LNA of the front end receiver is configured forincreased jammer suppression. For example, the LC tank circuit 402 ofthe LNA 400 is adjusted by controlling the switch banks 404, 406 toselectively enable capacitors of the capacitor bank 408 to shift the LCresonant frequency (higher or lower) away from the frequency of the selfjammer. In an exemplary embodiment, the baseband processor 108 outputsthe control signal 130 to control the switch banks 404, 406 to shift theresonant frequency of the LNA.

At block 506, a determination is made as to whether there are anyexternal jammers present to due transmissions in a communication bandfrom nearby devices. For example, in an exemplary embodiment, thebaseband processor 108 has knowledge of current external transmissionsfrom nearby devices based on other local receivers at the device. If anexternal jammer is present, the method proceeds to block 508. If anexternal jammer is not present, the method proceeds to block 510.

At block 508, the LNA of the front end receiver is configured forincreased jammer suppression. For example, the LC tank circuit 402 ofthe LNA 400 is adjusted by controlling the switch banks 404, 406 toselectively enable capacitors of the capacitor bank 408 to shift the LCresonant frequency (higher or lower) away from the frequency of theexternal jammer. In an exemplary embodiment, the baseband processor 108outputs the control signal 130 to control the switch banks 404, 406 toshift the resonant frequency of the LNA.

At block 510, a determination is made as to whether there are anyjammers present in a receive band, such as in a received GPS band. Forexample, in an exemplary embodiment, the jammer detector 132 detects forjammers in a received GPS band. If a received in-band jammer is present,the method proceeds to block 512. If a received in-band jammer is notpresent, the method proceeds to block 514.

At block 512, the LNA of the front end receiver is configured forincreased jammer suppression. For example, the LC tank circuit 402 ofthe LNA 400 is adjusted by controlling the switch banks 404, 406 toselectively enable capacitors of the capacitor bank 408 to shift the LCresonant frequency (higher or lower) away from the frequency of thereceived in-band jammer. In an exemplary embodiment, the jammer detector132 outputs the control signal 134 to control the switch banks 404, 406to shift the resonant frequency of the LNA.

At block 514, a determination is made as to whether there are anyexternal jammers present in the current geographic position of thedevice. For example, in an exemplary embodiment, the baseband processor108 has knowledge of the current device position by processing receivedGPS signals. The baseband processor 108 also has knowledge of potentialjammer signals in the current geographic region. For example, thebaseband processor 108 may receive this knowledge from a base station orother entity. If a jammer is present in the current geographic region,the method proceeds to block 516. If a jammer is not present in thecurrent geographic region, the method proceeds to block 518.

At block 516, the LNA of the front end receiver is configured forincreased jammer suppression. For example, the LC tank circuit 402 ofthe LNA 400 is adjusted by controlling the switch banks 404, 406 toselectively enable capacitors of the capacitor bank 408 to shift the LCresonant frequency (higher or lower) away from the frequency of thejammer in the current geographic region. In an exemplary embodiment, thebaseband processor 108 outputs the control signal 130 to control theswitch banks 404, 406 to shift the resonant frequency of the LNA.

At block 518, the LNA of the front end receiver is reconfigured fornormal operations at the appropriate resonant frequency. For example,the LC tank circuit 402 of the LNA 400 is adjusted to shift the LCresonant frequency back to the appropriate GPS resonant frequency (i.e.,GPS L1 shown in FIG. 2)

Accordingly, a reconfigurable LNA for use in a front end receiver isprovided. The LNA can be reconfigured to shift its resonant frequencyaway from detected self and/or external jammers thereby providingincreased jammer suppression.

FIG. 6 shows an exemplary embodiment of a reconfigurable LNA apparatus600. For example, the apparatus 600 is suitable for use as the LNA 400shown in FIG. 4. In an aspect, the apparatus 600 is implemented by oneor more modules configured to provide the functions as described herein.For example, in an aspect, each module comprises hardware and/orhardware executing software.

The apparatus 600 comprises a first module comprising means (602) fordetecting if a jammer is present, which in an aspect comprises thebaseband processor 108 or the jammer detector 132.

The apparatus 600 also comprises a second module comprising means (604)for tuning a resonant frequency of an LNA away from the jammer toincrease jammer rejection if the jammer is present, which in an aspectcomprises the switch banks 404 and 406 and capacitor bank 408.

The apparatus 600 also comprises a third module comprising means (606)for tuning the resonant frequency of the LNA to a selected operatingfrequency if the jammer is not present, which in an aspect comprises theswitch banks 404 and 406 and capacitor bank 408.

Those of skill in the art would understand that information and signalsmay be represented or processed using any of a variety of differenttechnologies and techniques. For example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof. It is further notedthat transistor types and technologies may be substituted, rearranged orotherwise modified to achieve the same results. For example, circuitsshown utilizing PMOS transistors may be modified to use NMOS transistorsand vice versa. Thus, the amplifiers disclosed herein may be realizedusing a variety of transistor types and technologies and are not limitedto those transistor types and technologies illustrated in the Drawings.For example, transistors types such as BJT, GaAs, MOSFET or any othertransistor technology may be used.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the exemplary embodiments of the invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a Digital SignalProcessor (DSP), an Application Specific Integrated Circuit (ASIC), aField Programmable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in Random Access Memory (RAM), flashmemory, Read Only Memory (ROM), Electrically Programmable ROM (EPROM),Electrically Erasable Programmable ROM (EEPROM), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes bothnon-transitory computer storage media and communication media includingany medium that facilitates transfer of a computer program from oneplace to another. A non-transitory storage media may be any availablemedia that can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

The description of the disclosed exemplary embodiments is provided toenable any person skilled in the art to make or use the invention.Various modifications to these exemplary embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the invention is not intended tobe limited to the exemplary embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. An apparatus comprising: an LNA having a tunableresonant frequency; and a detector configured to output a control signalthat is connected to the LNA and configured to tune the resonantfrequency of the LNA to increase jammer suppression.
 2. The apparatus ofclaim 1, the LNA comprising: an LC tank circuit comprising a capacitorbank; and at least one switch coupled to the capacitor bank toselectively enable at least one capacitor of the capacitor bank into theLC tank circuit based on the control signal to tune the resonantfrequency of the LNA.
 3. The apparatus of claim 1, the detectorcomprising a jammer detector configured to detect a jammer frequencyreceived in a receiver front end and output the control signal to tunethe resonant frequency of the LNA away from the jammer frequency.
 4. Theapparatus of claim 1, the detector comprising a processor configured todetect a transmitted self-jamming frequency and output the controlsignal to tune the resonant frequency of the LNA away from theself-jamming frequency.
 5. The apparatus of claim 1, the detectorcomprising a processor configured to detect a jammer frequency receivedin a communication band and output the control signal to tune theresonant frequency of the LNA away from the jammer frequency.
 6. Theapparatus of claim 1, the detector comprising a processor configured todetect a jammer frequency in a geographic location and output thecontrol signal to tune the resonant frequency of the LNA away from thejammer frequency.
 7. The apparatus of claim 1, the detector configuredto tune the resonant frequency of the LNA to a selected operatingfrequency when no jammers are detected.
 8. The apparatus of claim 1, theapparatus configured for use in a transceiver front end.
 9. Theapparatus of claim 1, the apparatus configured for use in a GlobalNavigation Satellite Systems (GNSS) receiver.
 10. A method comprising:detecting if a jammer is present at an LNA having a tunable resonantfrequency and outputting a control signal that is connected to the LNA;tuning a resonant frequency of the LNA away from the jammer in responseto the control signal to increase jammer rejection if the jammer ispresent; and tuning the resonant frequency of the LNA to a selectedoperating frequency in response to the control signal if the jammer isnot present.
 11. The method of claim 10, further comprising tuning theresonant frequency of the LNA using an LC tank circuit comprising acapacitor bank and at least one switch coupled to the capacitor bank toselectively enable at least one capacitor of the capacitor bank into theLC tank circuit based on a control signal.
 12. The method of claim 10,the detecting comprising: detecting a jammer frequency received by areceiver front end; and outputting control signal to tune the resonantfrequency of the LNA away from the jammer frequency.
 13. The method ofclaim 10, the detecting comprising: detecting a transmitted self-jammingfrequency; and outputting the control signal to tune the resonantfrequency of the LNA away from the self-jamming frequency.
 14. Themethod of claim 10, the detecting comprising: detecting a jammerfrequency received in a selected communication band; and outputting thecontrol signal to tune the resonant frequency of the LNA away from thejammer frequency.
 15. The method of claim 10, the detecting comprising:detecting a jammer frequency in a geographic location; and outputtingthe control signal to tune the resonant frequency of the LNA away fromthe jammer frequency.
 16. An apparatus comprising: means for detectingif a jammer is present at an LNA having a tunable resonant frequency;means for outputting a control signal that is connected to the LNA;means for tuning a resonant frequency of the LNA away from the jammer inresponse to the control signal to increase jammer rejection if thejammer is present; and means for tuning the resonant frequency of theLNA to a selected operating frequency in response to the control signalif the jammer is not present.
 17. The apparatus of claim 16, furthercomprising: means for detecting a selected jammer frequency; and meansfor outputting the control signal to tune the resonant frequency of theLNA away from the jammer frequency.
 18. The apparatus of claim 16,further comprising: means for detecting a transmitted self-jammingfrequency; and means for outputting the control signal to tune theresonant frequency of the LNA away from the self-jamming frequency. 19.The apparatus of claim 16, further comprising: means for detecting ajammer frequency received in a selected communication band; and meansfor outputting the control signal to tune the resonant frequency of theLNA away from the jammer frequency.
 20. The apparatus of claim 16,further comprising: means for detecting a jammer frequency in ageographic location; and means for outputting the control signal to tunethe resonant frequency of the LNA away from the jammer frequency.